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Discussion Starter #1
So this is my first post, out of all the forums my choice was yours. Best fitting, now that I own a 99 DX. Did the whole turbo AWD (dsm), muscle car gas gussler thing. Now looking forward to finally finding this car, the only 2000< Honda I liked.

I see D as economy or turbo potential.
Any way to get both?

Yes I have searched the topic, but am somethat overwhelmed with information not pertaining. Someone famish for detail. Just trying to peace this all together.

With all the options. d15b 3-stage, y8, z6.
With all these options of the D series, could you still boost a car and fall into lean burn parameters at cruise?
 

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1997 Civic Ex Turbo
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With a tune not aiming for fuel efficiency, my turbo d16y8 gets 35mpg and puts down 211whp. I could lean out the vacuum maps a little more and get better fuel efficiency. There are guys with 350-400whp that still get 35-40mpg outside of boost.
 

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ej8
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Your post has me lost.
What is your question?

Most turbo d motors get above normal mpg which is aroubd 28-30mpg.
Now all that depends on how you drive.
Im turbo and i get around 30mpg with boosting here n there. Also im still odb2 so i cant always be as lean as id like off boost.

So your question again is?
 

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'89 CRX HF
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It's definitely going to depend on your driving habits. I average 42-ish mpg highway, with an all time high of 51mpg leaning it out and adding timing. However if you are like most turbo guys with a heavy foot, you won't see near those numbers.
 

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Honda City
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Medium to Big turbo, lean burn out of boost. Use pistons with lots of quench and a Y8 head. Skip the 3 stage VTEC BS since it's a pain to tune them. Switch to OBD1. Use a D16Z6 or Y8 block to have good piston/rod options. Tight quench with lean burn out of boost.
 

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78 MPG has been achieved lean burning a 450 HP d. 20:1 afr in cruise, spark plug mods, 230 degree thermostat, blocked off Rad, taped all body lines in front, etc.
 

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Discussion Starter #8
OK so Y8 head swap, or just a full engine for upgraded positions. I get that.
What I don't get is the matching of cam (if even req.) and fuel management system.
What about the ecu, what system would best manage that?
If i go y8 head or engine, it's OBDII (a match with current d16y7)

To be having all that extra sensor informations seem like it would help tune, however I see OB DI said to be only option?

And I do understand the none engine related fuel efficiency effects. EPA rated stock @ 34mpg. I would like maintain at lest 34 without fixing that (goal would be 45+ mpg) But lets leave all that crap aside for the sake of this discussion.
 

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Discussion Starter #9
Medium to Big turbo, lean burn out of boost. Use pistons with lots of quench and a Y8 head. Skip the 3 stage VTEC BS since it's a pain to tune them. Switch to OBD1. Use a D16Z6 or Y8 block to have good piston/rod options. Tight quench with lean burn out of boost.

How would the effect of a smaller turbo change under normal cruise compared to a larger one? I understand the spool, load and boost. But why put a larger wheeled, heavy and more hard to move compressor in the way of the flow? Sounds like thats counter productive.

under normal cruise load, what would the effect of a t25 be vs larger?
 

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with a small turbo you would go into boost alot more then you would want to. it would depend where you are and where you need to drive too obviously climbing big hills you might want to get in boost for some of the bigger hills.
 

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Discussion Starter #11
Well if I stayed in the tradition of hypermiling, then I would downshift the hills and try to keep a vacuum.

somthing like that, right?
 

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my turbo z6 is tune for lean cruising and part throttle..

17-18 afr when crusing, 15-16 afr during light throttle, 14-13 afr from 1-3.5krpm full throttle without boost. my boosting started to come on at 4.2krpm.

im getting similar gas mileage as stock
 

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ej8
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Getting into boost is all up to how ypu drive.
My nissan t25 spools fast around 3k, but i can do freeway driving and not get into boost or only crack a few psi for a second.

And aem fic works for obd2.
And harder to tune with obd2 then obd1. As you said more sensor but thats also more things to keep happy since obd2 was manily made for emission.

And power, mpg, and Safety of the motor is all in the tune and how ypu drive it.
 

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The Wife and the Car
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A good turbo build can give you better mileage than the best NA build.
First pick your cruise RPM?. In my case say 3500 RPM.
At this point you want to be making about 2-3 PSI of boost. Ive found 2-3 PSI to be the optimum for mileage. Then tune your part throtel for 18:1 at this point.
Make it a point to get into as a high a gear as possible. Then cruise down the road at 18:1 your in top gear, about 2 PSI on the boost gauge. Best we got was about 22 Km/Ltr on an inter city drive. Keep aggressive trims on your coolant and IATs. i.e. if the temps cross 90c start to add more gas.
The Honda engine is one of the best engines you can get in the world for such a lean burn setup. Thanks to the swirl and tumble of the Y8 head. I would not pick a z6 head. Cause deto tends to set in much faster. Than on a y8 head. Which can take a lot of abuse in terms of temps and leanness of AFR before deto starts.
Honda are kings when it comes to engine efficiency, lean burn and high CR. It all started with the VF750 Honda bike. Read up on how they where the first to offer high CR on pump with the VF750 engine. What you get in your y8 head is 10 years of more evolution than what was on the 750 head sold in 84.
 

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Brokedick Millionaire
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VW/Audi has their tuning set for best mileage if you can stay at or below zero boost/vacuum. At that point the turbo isn't really doing any work but still assisting airflow.

which all helps lower pumping loses and increase gas mileage.
 

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1997 Civic Ex Turbo
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A good turbo build can give you better mileage than the best NA build.
First pick your cruise RPM?. In my case say 3500 RPM.
At this point you want to be making about 2-3 PSI of boost. Ive found 2-3 PSI to be the optimum for mileage. Then tune your part throtel for 18:1 at this point.
Make it a point to get into as a high a gear as possible. Then cruise down the road at 18:1 your in top gear, about 2 PSI on the boost gauge. Best we got was about 22 Km/Ltr on an inter city drive. Keep aggressive trims on your coolant and IATs. i.e. if the temps cross 90c start to add more gas.
The Honda engine is one of the best engines you can get in the world for such a lean burn setup. Thanks to the swirl and tumble of the Y8 head. I would not pick a z6 head. Cause deto tends to set in much faster. Than on a y8 head. Which can take a lot of abuse in terms of temps and leanness of AFR before deto starts.
Honda are kings when it comes to engine efficiency, lean burn and high CR. It all started with the VF750 Honda bike. Read up on how they where the first to offer high CR on pump with the VF750 engine. What you get in your y8 head is 10 years of more evolution than what was on the 750 head sold in 84.
Could you explain how you'd get better fuel efficiency at 2-3 psi of boost than at -15inmg? I'd like to know how this could be.
 

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ej8
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Could you explain how you'd get better fuel efficiency at 2-3 psi of boost than at -15inmg? I'd like to know how this could be.
Think of it like this.
The in vac the motor is suck as hard as it can working alot.
While.at very low psi its not really working. Thr turbo is pushing air n, but low psi mean 12s afr. Which isnt to much fuel or work on the motor.
 

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There was this guy that was running a 3 stage that he would tune it to run closest to 0 psi at 12v mode running a lean burn and claimed to get like 60 mpg. he was pushing like 240 HP. Simple theory is 0 psi = no boost but also no pumping loss, giving the best mpg.
 
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